Operation of Meshed Hybrid Microgrid During Adverse Grid Conditions With Storage Integrated Smart Transformer

Abstract

Microgrid faces various challenges such as reverse power flow, peak power demand, voltage limit violations, etc., due to significant installations of renewable energy sources (RESs) and electric vehicles (EVs). For continuous and effective operation of such a system, enhanced and complex control methodologies are needed. Smart transformer (ST) has emerged as a promising solution for overcoming such challenging issues. This paper proposes the operation of battery energy storage system (BESS) integrated ST in a meshed hybrid microgrid. Instead of connecting through ac interconnections with normally open (NO) circuit breakers (CBs), the same line is connected through the medium voltage (MV) dc links of ST. This introduces several paths for controlled power flow in the system. As compared to ac interconnections, this configuration improves the performance of the overall system during various adverse operating conditions such as reverse power flow, peak power demand, and voltage sag. Moreover, the MVDC line voltage is controlled by one ST, resulting in reduced control complexity of other power converters. Detailed simulation and experimental results are provided to show the merits of the proposed system.INDEX TERMS Microgrid, photovoltaic (PV) integration, Smart transformer (ST).

Review of Smart Transformer-Based Meshed Hybrid Microgrids: Shaping, Topology and Energy Management Systems

“…Nonetheless, MHMs must integrate supervisory control coupled with an Energy Management System (EMS) to optimize network performance in terms of power quality, reduced line losses, and MG fault management capability [14]. Recently, EMS strategies have been proposed in MHM that integrate ESS and PVG in connection and disconnection maneuvers [29] [30]. Similarly, they have shown that voltage and load profile control can be realized by meshing the network in a ring configuration with bidirectional power flow control [14], facilitating independent active and reactive power management [31].…”

“…This index is adjusted by the power flow controller according to the required voltage level at both 𝑀𝑉 𝐷𝐶 and 𝐿𝑉 𝐷𝐶 from the conditions set by the power reference block and operating mode of the SST, which set the reference 𝑀𝑉 𝐷𝐶 𝑟 and 𝐿𝑉 𝐷𝐶 𝑟 . The functionality of the DAB coupled to the control layers allows integrating, typically, ESS on the 𝑀𝑉 𝐷𝐶 bus [33], even allowing to form of hybrid 𝐴𝐶 − 𝐷𝐶 loops by integrating DER on the 𝐿𝑉 𝐷𝐶 bus port [25]. The third stage of the SST enables the connection of the MG to the SST and bidirectional power transfer between 𝐿𝑉 𝐷𝐶 and 𝐿𝑉 𝐴𝐶 .…”

“…With this, it could be shown that the duration of ESS operation in island mode is increased by intentionally decreasing the 𝐿𝑉 𝐴𝐶 voltage by the ST in a MHM. Under this approach in [30], it was possible to demonstrate the conformation of several pathways for the controlled power flow in the system. Compared to AC interconnects, this configuration improves the entire system's performance during various adverse operating conditions, such as reverse power flow, peak power demand, and voltage drop, as the operation of an integrated ESS in an MHM is proposed.…”

“…In [32], a rulebased EMS is proposed to establish the reconnection of the MHM to the MV AC grid while keeping the ST converter running, thus initiating the power flow and establishing the transition from isolated to grid-connected mode of the MHM. A similar approach is presented in [33] and [29], in which MHM management mechanisms are proposed to operate the integrated ESS, ST in an MHM. Instead of connecting through AC interconnects with normally open circuit breakers, the same line is connected through the MV DC ST DC links introduce several ways for the controlled flow of power in the system in an optimal way.…”

“…These probabilistic models determine the constraints when presenting the RO problem, whose solution must be feasible in the uncertainty space defined by each DER of the MHM [53] [54]. By determining the set of feasible solutions through solving the optimization problem, the performance of the target MHM can be evaluated under an emulation scheme with specialized hardware as proposed in [29] [30][56] [47]. Finally, according to the results achieved at the prefeasibility level, we seek to establish the technical and economic feasibility of the potential integration of an STbased MHM with high penetration of DG, V2G, and ESS in a DS operated by an OEMS.…”